DIC Experimental Study On Local Buckling Of Rectangular Concrete-filled Steel Tubular Plates

Plates are important components of engineering structures and mainly bear compressive and bending loads during service.Similar to rods,plates also have compression stability issues.For plates with large width to thickness ratios,local buckling is prone to occur under compressive and bending loads,which affects ultimate bearing capacity.Although there have been many studies on elastic and elastic-plastic buckling of plates,further research is still necessitated on the mode evolution of local buckling process of plates and the variation laws in the deflection surface during the post-buckling stage.This study conducted axial compression tests on wall panels of steel tube and resin tube,and used digital image correlation(DIC)technology to visually monitor the compression buckling process of the panels.The equilibrium path and deflection curve function of the post-buckling stage were obtained.In addition,based on the recommendations of the North American standard ANSI and other researchers,a formula for calculating the effective width of the plate is advised,providing a basis for the utilization of the post buckling strength of the plate.The research results are as follows:(1)DIC axial compression tests were conducted on steel pipe and resin pipe fittings with free and unilateral restrained plates,and the mechanical performance parameters such as stiffness,displacement ductility,and ultimate bearing capacity of each specimen were obtained.The experimental results show that,at the same cross-sectional size,with the panel thickness increases,the width to thickness ratio decreases,and the ultimate bearing capacity of the steel pipe and resin pipe fittings is significantly improved;Under the same aspect ratio,when there are certain constraints inside the specimen,its ultimate bearing capacity can be increased by about 25% for steel pipe specimens and more than 60% for resin pipe specimens;A specimen with a larger width to thickness ratio has better ductility,but internal support will reduce the ductility of the specimen and alter its load-bearing performance.(2)3D-DIC technology can achieve visual research on the buckling modes evolution process of plate.By extracting and analyzing the buckling modes at different loading times,the post-buckling equilibrium path of the plate can be established,and the critical buckling load test value can be obtained.In order to verify the accuracy of this value,theoretical calculations and comparisons were conducted using the mechanical performance parameters determined by steel and resin material property tests.Finally,the variation law and deflection curve equation of the stable mode in post-buckling stage of the plate were obtained.By analyzing the buckling modes of each plate,it can be concluded that the continued loadbearing capacity of resin tube specimens in post-buckling is much higher than that of steel tube;The unilateral constraint filled internally changes the buckling mode of the plate,allowing it to only deform outside the convex surface far from the constraint.The number and location of buckling waves are more random compared to free plates.Moreover,the displacement outside the plane of each buckling wave will continuously increase with the increase of applied load,but each waveform does not increase to the same extent and does not strictly follow the theoretical division of proportional positions.This is particularly evident during the buckling process of steel tube.The existence of internal unilateral constraints can enhance the critical buckling load and post-buckling ultimate capacity of the plate,and the enhancement effect increases with the increase of the tightness of constraint.(3)Verify the accuracy of the effective width test values obtained in this study based on ANSI and domestic thin-walled standard.Due to the redundant parameters required to calculate the effective width calculation formula in the domestic thin-walled standard,and the complex calculation process,the effective width calculation formula proposed in the study is based on the ANSI and the effective width calculation formula suggested by other researchers.To verify the accuracy of the formula,comparative analysis was conducted on the test results of other literature and corresponding suggested formulas.The results indicate that the effective width formula advised in this study has more accurate predictability compared to the formulas existing in the literature.